1. Field of the Invention
The present invention relates to high-speed integrated communication network of an asynchronous transfer mode (ATM) of packetized cells, and in particular, to call control comprising admission control for connection requests from information sources and transmission control of the packetized cells from the information sources of admitted or accepted connection requests to a transmission line required by the admitted connection requests.
2. Description of the Prior Art
In a known digital communication network, a packet multiplex technique is used where digital information is packetized into a plurality of packets or cells each comprising a section of the digital information of a fixed bit length with a header or a label for ensuring discrimination of the information source and destination. The packets are transmitted on the required transmission line by the time-division multiplex technique.
In an integrated communication network for various services such as telephone, data, and videocommunication services, the ATM technique is used for time-division multiplexing packets from different sources such as a telephone set, a personal computer and a video camera device on the required transmission line. There is difference in bit rates between information signals from those sources and therefore, packet delivery rates are different between those sources. Accordingly, packets of information of a high-bit rate signal are more frequently inserted into time slots in comparison with packets of information of a slow-bit rate signal by the ATM technique.
A packet network using the ATM technique is disclosed in a paper by A. Thomas et al entitled "ASYNCHRONOUS TIME-DIVISION TECHNIQUES: AN EXPERIMENTAL PACKET NETWORK INTEGRATING VIDEOCOMMUNICATION" published at ISS (International Switching Symposium) '84 florence, 7-11 May 1984 (Reference I), another paper by Woodruff et al entitled "A CONGESTION CONTROL FRAMEWORK FOR HIGH-SPEED INTEGRATED PACKETIZED TRANSPORT", P.P. 7.1.1.-7.1.5. CH2535-3/88/0000-0203,IEEE 1989 (Reference II), another paper by Schaffer entitled "SYNCHRONOUS AND ASYNCHRONOUS TRANSFER MODES IN THE FUTURE BROADBAND ISDN", P.P. 47.6.1-47.7.6.7. CH2538-7/88/0000-1552, IEEE 1988 (Reference III), and others.
It is needless to say that a transmission line has a transmission capacity or a predetermined bandwidth. While, a part of the transmission capacity is used for transferring information from a source. Accordingly, the number of source simultaneously using a single transmission line is restricted by the capacity of the transmission line and a bandwidth demanded for transferring information of respective sources. Therefore, when a new connection request is originated from a source for using a transmission line, admission control is performed in order to decide whether the new connection request is accepted or rejected.
The decision to admit the new connection is based on whether a required transport performance can be maintained or not. The required transport performance is dependent on traffic descriptors for the requested connection's traffic flow characteristics, such as average bandwidth, peak bandwidth, burstiness, etc.
In a conventional method, a virtual bandwidth is used as a parameter of the required transport perfomance and is defined for the requested connection as a value between the connection's average and peak rate.
When a new connection request is originated from an information source, a virtual bandwidth of the new connection is determined from the connection's descriptors and is compared with a residual bandwidth which is difference between the predetermined bandwidth of the transmission line and a sum of virtual bandwidths of connections already using the transmission line. When the virtual bandwidth of the new connection is smaller than the residual virtual bandwidth, the new connection request is accepted and a virtual circuit is set up over the network including the transmission line. Then, the packets from the information source are transferred through the virtual circuit.
On the other hand, when the virtual bandwidth of the new connection is larger than the residual bandwidth, the new connection request is rejected.
It is usual that a packet delivery rate in each connection varies. Therefore, the required transport performances of the accepted connections are badly effected from each other.
A bandwidth for each connection can be decided based on the peak rate or the maximum rate of the connection. Although the transport performance is maintained, a bandwidth efficiency is degraded because the packet rate is usually lower than the peak rate.